Variable mode jet engin - suitable for STOVL

ABSTRACT

This jet engine comprises of a complete low bypass turbofan unit  1  including secondary fan unit  2  and engine core, ahead of which sits a larger diameter main fan unit  3  driven from the front of the secondary fan via a long drive shaft  4.  A center portion of the main fan would feed the secondary fan via long central duct  5.  The outer portion of the main fan would be ducted into a split exhaust plenum chamber  6.  This chamber has thrust vectoring exhaust mechanisms  7  immediately attached to each side, and then each side then feeds a thrust splitter  10,  and then feeds to variable area outer ducting  8,  using double-hinged inner and outer doors  9.  Both outer ducts would rejoin the central duct downstream in a second plenum chamber  11  just ahead of the secondary fan. Between this chamber and secondary fan would be an intercooler  12.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

REFERENCE TO MICROFICHE APPENDIX

[0003] Not Applicable

BACKGROUND OF THE INVENTION

[0004] This invention relates to a variable mode (turbofan, turbojet, ramjet) type jet engine, which is also suitable for short takeoff vertical landing (STOVL). Jet engines are normally built in fixed mode either as turbofans, turbojets or ramjets, this invention sets out to combine all types of engine, plus inclusion of STOVL capability.

BRIEF SUMMARY OF THE INVENTION

[0005] According to the present invention there is provided a jet engine comprising of a complete low bypass turbofan unit to the rear, including a (secondary) fan unit and engine core (compressors, combustion chamber, turbines and secondary bypass duct), some eight to thirteen feet ahead of which sits a larger diameter (main) fan unit, driven from the front of the secondary fan via a long drive shaft. A centre portion of the main fan would feed the secondary fan via a long central duct of roughly the same area as the secondary fan. The outer portion of the airflow from the main fan would be ducted into a split exhaust plenum chamber immediately to the rear of the main fan. This chamber would have forward mounted thrust vectoring exhaust mechanisms immediately attached to either side, and then each side would feed into variable area outer ducting, using inner and outer double-hinged doors, on either side of the engine. These doors would be arranged to be able to split the thrust from the main fan, so as to exhaust either outwards or inwards forming a ram into the secondary fan. Both outer ducts would then rejoin the long central duct downstream in a second plenum chamber just ahead of the secondary fan. Between this second chamber and the secondary fan would be space to fit an in line intercooling device to cool down the incoming air charge.

BRIEF DESCRIPTION OF THE SEVERAL VEIWS OF THE DRAWING

[0006]FIG. 1 illustrates the low bypass turbofan/ramjet mode (ramfan); the outer ducting doors would be fully open, ramming the airflow from the main fan into the secondary fan, hence supercharging the secondary fan and engine core at subsonic speeds, and forming a ramjet at supersonic speeds, albeit with rotating inner parts. There would be no need for an afterburner on this type of engine.

[0007]FIG. 2 illustrates the transition between modes and intermediate bypass mode; at subsonic speeds the outer ducting doors would be set to the mid position, splitting the outer portion of the main fan thrust and thereby only partially supercharging and partially bypassing the secondary fan and engine core.

[0008]FIG. 3 illustrates the high bypass turbofan mode; at subsonic speeds the outer ducting doors would be fully closed, allowing the outer portion of the main fan to completely bypass the secondary fan and engine core.

[0009]FIG. 3A illustrates the high bypass turbofan/STOVL mode; at low speeds with the outer ducting doors fully closed, the forward mounted thrust vectoring exhaust mechanisms can be deflected downwards along with the rear variable area nozzle.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Referring to the drawing there is provided a jet engine comprising of a complete low bypass turbofan unit 1 to the rear of the airframe, including (secondary) fan unit 2 and engine core (compressors, combustion chamber, turbines and secondary bypass duct 15), some eight to thirteen feet ahead of which sits a larger diameter (main) fan unit 3, driven from the front of the secondary fan via a long drive shaft 4. A centre portion of the main fan would feed the secondary fan via a long central duct 5 which would be of roughly the same area as the secondary fan. See FIGS. 1 and 2.

[0011] The outer portion of the airflow from the main fan would be ducted into a split exhaust plenum chamber 6 immediately to the rear of the main fan. This chamber would have forward mounted thrust vectoring exhaust mechanisms 7 immediately attached to either side, and then each side would feed into variable area outer ducting 8 using inner and outer double-hinged doors 9 on either side of the engine. These doors would be arranged to be able to split the thrust 10 from the main fan, so as to exhaust either outwards or inwards forming a ram into the secondary fan. Both outer ducts would then rejoin the long central duct downstream in a second plenum chamber II just ahead of the secondary fan 2. See FIG. 2.

[0012] Between this second chamber 11 and the secondary fan 2 would be space to fit an in line intercooling device 12 fitted in or around the rear of the central tube so as to cool down the incoming air charge. The engine core would have a two-stage combustion chamber 13 to ignite the extra oxygen provided by the main fan supercharging effect in low bypass turbofan mode. The rear exhaust nozzle 14 would be both variable in area and thrust vectoring. See FIGS. 1, 2 and 3A.

[0013] The ideal main bypass ratio for this type of engine would be around 1.6:1. The ideal secondary bypass ratio for this type of engine would be zero, but this would not allow for cooling of the engine core and rear exhaust. The large main fan in this design has in effect replaced the afterburner normally provided for on a conventional low bypass turbofan. Below are some typical figures for this type of engine: - Main fan diameter 46 inches Secondary fan diameter 28 inches Main bypass ratio 1.35:1 Secondary bypass ratio 0.20:1 Static power from main fan 13500 pounds (High bypass turbofan mode) Static power from rear turbofan 13500 pounds (High bypass turbofan mode) Thrust split-front/rear 50%/50% Static combined power 27000 pounds (High bypass turbofan mode) Static combined power 40500 pounds (Supercharged low bypass turbofan mode) 

1. What I claim as my invention is a jet engine comprising of a complete low bypass turbofan unit to the rear including (secondary) fan unit and engine core (compressors, combustion chamber, turbines and secondary bypass duct), some eight to thirteen feet ahead of which sits a larger diameter (main) fan unit driven from the front of the secondary fan by a long drive shaft, a centre portion of the main fan would feed the secondary fan via a long central duct of roughly the same area as the secondary fan, the outer portion of the airflow from the main fan would be ducted into a split exhaust plenum chamber immediately to the rear of the main fan unit, this chamber would have forward mounted thrust vectoring exhaust mechanisms immediately attached to each side, and then each side would feed into variable area outer ducting using inner and outer double-hinged doors on either side of the engine, these doors would be arranged so as to be able to split the thrust from the main fan and to exhaust either outwards or inwards forming a ram into the secondary fan, both outer ducts would then rejoin the long central duct downstream in a second plenum chamber just ahead of the secondary fan, between this second chamber and the secondary fan would be space to fit an in line intercooling device.
 2. A jet engine as claimed in claim 1 wherein there is provided for a main fan or fans placed ahead of the aircraft centre of gravity and driven by a long shaft or shafts from the engines smaller diameter secondary fan or fans and engine core, which are located at the rear of the airframe behind the aircraft centre of gravity, the main fan or fans and secondary fan or fans/engine core are two completely separate engine units.
 3. A jet engine as claimed in claim 2 wherein there is provided for a long central duct of the same diameter as the secondary fan or fans connecting the main fan or fans to the secondary fan or fans so as to feed the secondary fan or fans and engine core with a portion of the airflow from the centre of the main fan or fans
 4. A jet engine as claimed in claim 3 wherein the long central duct is part of the airframe construction and would be surrounded by an integral fuel tank located around the aircraft centre of gravity.
 5. A jet engine as claimed in claim 4 wherein there is provided for an annular plenum chamber mounted directly to the rear of the main fan or fans featuring a split exhaust system ejecting from either side of the main fan or fans, this chamber would exclude the portion of airflow directed into the long central duct and would form an integral part of the airframe construction.
 6. A jet engine as claimed in claim 5 wherein there are provided for two forward mounted thrust vectoring exhaust mechanisms placed on either side of the plenum chamber and arranged so as to exhaust either rearwards or downwards, these mechanisms would form the forward part of the outer ducting and be part of the airframe and would be first canted downwards and then towards the rear.
 7. A jet engine as claimed in claim 6 wherein there are provided for two variable area outer bypass ducts placed immediately behind the forward mounted thrust vectoring exhaust mechanisms on either side of the engine, these ducts would gradually curve upwards towards the rear so as to rejoin the long central duct at its rearwards end.
 8. A jet engine as claimed in claim 7 wherein the variable area outer bypass ducts are an integral part of the airframe construction and are positioned lower than the main fan so as to form a tunnel under the airframe and to produce a cushion of air in VTOL mode.
 9. A jet engine as claimed in claim 8 wherein there are provided for inner and outer doors fitted to the variable area outer bypass ducts, the outer doors would be hinged at the rear with the inner doors fitted to the forward part of the outer doors using a second hinge, a third hinge would be fitted to the inner doors, about three-quarters towards the rear, this arrangement will provide for a constant variable area ducting.
 10. A jet engine as claimed in claim 9 wherein there are provided for thrust splitting devices fitted to the forward part of the inner and outer doors, immediately behind the forward mounted thrust vectoring exhaust mechanisms, and arranged so as to split the airflow either outwards, or inwards so that the inner doors form a ram into the secondary fan or fans.
 11. A jet engine as claimed in all previous claims wherein there could be provided for a single outer bypass ducting system only, instead of two ducts, this single outer duct would be fitted to the underside of the airframe directly beneath the long central duct, and would be an integral airframe component.
 12. A jet engine as claimed in all previous claims wherein there is provided for a second plenum chamber at the joint between the outer bypass ducts and the long central duct just ahead of the secondary fan, this chamber would form part of the central duct and would be an airframe component.
 13. A jet engine as claimed in claim 12 wherein there is provided for an intercooling device fitted in or around the long central duct and between the second plenum chamber and the secondary fan or fans and engine core, to cool down the incoming air charge.
 14. A jet engine as claimed in claim 13 wherein there is provided for a secondary bypass duct fitted behind the secondary fan or fans and around the engine core.
 15. A jet engine as claimed in claim 14 wherein there is provided for a two-stage combustion chamber within the engine core.
 16. A jet engine as claimed in claim 15 wherein there is provided for a rear mounted thrust vectoring variable area nozzle, with the fixed end fitted to the rear of the engine secondary bypass duct and arranged so as to vector the thrust rearwards or downwards and to be of a smaller diameter than the secondary bypass duct when fully closed.
 17. A jet engine arrangement substantially as described herein with reference to FIGS. 1, 2, 3 and 3A of the accompanying drawings. 